1. Field of the Invention
On exposure to harsh conditions, such as under hydrothermal reaction, an interlayer cross-linked clay generally ceases to retain its stability on account of a decrease in the interlayer distance, for example.
This invention relates to a method for stably retaining an interlayer cross-linked clay under a hydrothermal reaction and a method for producing an interlayer cross-linked clay which is stable even under a hydrothermal reaction.
2. Description of the Prior Art
U.S. Pat. Nos. 4,629,713, 4,753,908, 5,084,428, 5,087,598, 5,214,012, and 5,369,069, which cover inventions concerning interlayer cross-linked clay, were issued to inventors including Kenzi Suzuki, the inventor of the instant patent application, and U.S. Pat. No. 4,839,318, also relating to an interlayer cross-linked clay, was issued to the same assignee as that of the instant patent application.
Neither a method for stably retaining an interlayer cross-linked clay under a hydrothermal reaction nor a method for producing an interlayer cross-linked clay which is stably retained even under a hydrothermal reaction has been known in the art.
First, an interlayer cross-linked clay will be described in detail below.
An interlayer cross-linked clay is synthesized by introducing pillars of an inorganic oxide such as alumina or zirconia between layers of the silicate of a clay mineral which possesses a swelling property. The interlayer distance, which is equivalent to pore diameter, equals the size of the pillars and ranges from several to some tens of .ANG.ngstroms. Interlayer cross-linked clays resemble zeolites in the size of pore diameter and the chemical properties. Attempts are therefore being made to utilize it for catalysts, catalyst carriers, separating materials, adsorbents, and the like for which zeolites have been commonly used to date. Interlayer cross-linked clays used for these products can be expected to be exposed to various ambient conditions. It may, for example, be used in a cooled or heated state or utilized even under a hydrothermal reaction. Frequently the interlayer cross-linked clay, when left standing at an elevated temperature or in the presence of a hydrothermal reaction, suffers an extreme decrease in surface area or pore volume to the extent of seriously hindering its usefulness.
A strong need is felt for the development of a method which enables an interlayer cross-linked clay of ordinary quality to be retained stably in the presence of a hydrothermal reaction and a special interlayer cross-linked clay which is capable of being stably retained under the presence of a hydrothermal reaction.
The present inventor continued a study with a view to meeting this need and has perfected this invention as a result.